I have a small number of batteries that when I put them in my charger (forget the name, but a smart one) it reads "Null," and it won't charge the cells.
Once, I got the charger to wake up and charge the battery, by removing the battery and putting it back in. I've not yet been able to repeat that lucky success.
My understanding is that once a battery drops below a certain voltage, the charger considers the battery faulty, and by design it won't charge a faulty battery.
Any way around this?
The problem stems from batteries left in forgotten flashlights or other devices. Left in there too long, they lose all or most of their charge and the smart charger won't accept them.